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Concomitant use of multiple drugs in most patients with cancer may result in drug-drug interactions (DDIs), potentially causing serious adverse effects. These patients often experience unrelieved cancer-related pain (CRP) during and after cancer treatment, which can lead to a reduced quality of life. Opioids can be used as part of a multimodal pain management strategy when non-opioid analgesics are not providing adequate pain relief, not tolerated, or are contraindicated. However, due to their narrow therapeutic window, opioids are more susceptible to adverse events when a DDI occurs. Clinically relevant DDIs with opioids are usually pharmacokinetic, mainly occurring via metabolism by cytochrome P450 (CYP). This article aims to provide an overview of potential DDIs with opioids often used in the treatment of moderate-to-severe CRP and commonly used anticancer drugs such as chemotherapeutics, tyrosine kinase inhibitors (TKIs), or biologics. A DDI-checker tool was used to contextualize the tool-informed DDI assessment outcomes with clinical implications and practice. The findings were compared to observations from a literature search conducted in Embase and PubMed to identify clinical evidence for these potential DDIs. The limited results mainly included case studies and retrospective reviews. Some potential DDIs on the DDI-checker were aligned with literature findings, while others were contradictory. In conclusion, while DDI-checkers are useful tools in identifying potential DDIs, it is necessary to incorporate literature verification and comprehensive clinical assessment of the patient before implementing tool-informed decisions in clinical practice., (© The Author(s) 2024. Published by Oxford University Press.)

Background: Cancer pain has a significant impact on patient's quality of life. Astrocytes play an important role in cancer pain signaling. The direct targeting of astrocytes can effectively suppress cancer pain, however, they can cause many side effects. Therefore, there is an urgent need to identify the specific signaling pathways or proteins involved within astrocytes in cancer pain as targets for treating pain., Methods: A neuropathic cancer pain (NCP) model was established by inoculating mouse S-180 sarcoma cells around the right sciatic nerve in C57BL/6 mice. Spontaneous persistent pain and paw withdrawal thresholds were measured using von Frey filaments. The NCP spinal cord dorsal horn (L4-L6) and mouse astrocyte cell line MA-C were used to study protein palmitoylation using acyl-biotin exchange, real-time polymerase chain reaction, ELISA, western blotting, and immunofluorescent staining., Results: In a cancer pain model, along with tumor growth, peripheral nerve tissue invasion, and cancer pain onset, astrocytes in the dorsal horn of the spinal cord were activated and palmitoyltransferase ZDHHC23 expression was upregulated, leading to increased palmitoylation levels of GFAP and increased secretion of inflammatory factors, such as (C-X-C motif) ligand (CXCL)10 (CXCL-10), interleukin 6, and granulocyte-macrophage colony-stimulating factor. These factors in turn activate astrocytes by activating the signal transducer and activator of transcription 3 (STAT3) signaling pathway. A competitive peptide targeting GFAP palmitoylations was designed to effectively alleviate morphine tolerance in cancer pain treatment as well as cancer pain signaling and inflammatory factor secretion., Conclusions: In a rodent model, targeting GFAP palmitoylation appears to be an effective strategy in relieving cancer pain and morphine tolerance. Human translational research is warranted., Competing Interests: Competing interests: None declared., (© American Society of Regional Anesthesia & Pain Medicine 2024. Re-use permitted under CC BY-NC. No commercial re-use. Published by BMJ.)

Chronic pain often coincides with changes in gut microbiota composition. Yet, the role of gut microbiota in bone cancer pain (BCP) is still not fully understood. This study investigated the role of gut microbiota in BCP and the effect of oxymatrine (OMT) on gut microbiota in BCP. A BCP mice model was developed to assess gut microbiota composition, serum and brain tissue butyric acid levels, and blood-brain barrier (BBB) permeability. Microbiota transplantation was used to restore gut microbiota, and the effect of Clostridium butyricum or sodium butyrate (NaB) supplementation on pain-related behaviors and BBB integrity was evaluated. The potential benefits of OMT on gut microbiota composition, peroxisome proliferator-activated receptor gamma (PPARγ)/cyclooxygenase-2 (COX-2) signaling, BBB integrity, and pain-related behaviors were also explored. BCP significantly altered gut microbiota composition and reduced serum and brain tissue butyric acid levels. Additionally, BBB permeability increased considerably in the BCP group compared with sham and control mice. Microbiota transplantation, as well as C butyricum or NaB supplementation, ameliorated pain-related behaviors and BBB integrity; the supplementation of C butyricum or NaB boosted brain-tight-junction protein expression, potentially through modulating PPARγ/COX-2 signaling. OMT influenced gut microbiota composition and regulated PPARγ/COX-2 signaling in the BCP model, improving pain-related behaviors and BBB integrity. BCP affects gut microbiota composition and butyric acid levels. Modulating gut microbiota and butyric acid levels through transplantation or supplementation may alleviate BCP. OMT shows potential as a treatment by altering gut microbiota composition and regulating PPARγ/COX-2 signaling. These findings provide new insights into BCP pathophysiology and possible treatments. PERSPECTIVE: This study explores the impact of gut microbiota on BCP. Microbiota transplantation alleviates BCP and enhances BBB integrity. Also, C butyricum or NaB improves BBB via PPARγ/COX-2. OMT, a BCP treatment, modifies microbiota by regulating PPARγ/COX-2, in turn improving pain and BBB integrity. These findings suggest a therapeutic approach, emphasizing clinical relevance in targeting gut microbiota and restoring butyric acid levels., (Copyright © 2024 United States Association for the Study of Pain, Inc. Published by Elsevier Inc. All rights reserved.)

Currently, the clinical treatment of bone cancer pain (BCP) is mainly related to its pathogenesis. The aim of the present study was to elucidate the potential role of N6-methyladenosine (m6A) in BCP in the spinal cord dorsal root ganglia (DRG) of BCP rats and its specific regulatory mechanism in N-methyl-d-aspartate receptor subunit 2B (NR2B). A rat model of BCP was constructed by tibial injection of Walker256 cells, and ALKBH5 and NR2B expression in the spinal cord DRG was detected. ALKBH5 was silenced or overexpressed in PC12 cells to verify the regulatory effect of ALKBH5 on NR2B. The specific mechanism underlying the interaction between ALKBH5 and NR2B was investigated using methylated RNA immunoprecipitation and dual-luciferase reporter gene assays. The results showed increased expression of m6A, decreased expression of ALKBH5, and increased expression of NR2B in the DRG of the BCP rat model. Overexpression of ALKBH5 inhibited NR2B expression, whereas interference with ALKBH5 caused an increase in NR2B expression. In NR2B, interference with ALKBH5 caused an increase in m6A modification, which caused an increase in NR2B. Taken together, ALKBH5 affected the expression of NR2B by influencing the stability of the m6A modification site of central NR2B, revealing that ALKBH5 is a therapeutic target for BCP., (© 2024 International Union of Biochemistry and Molecular Biology, Inc.)

Bone cancer pain (BCP) is a complex clinical challenge, with current treatments often falling short of providing adequate relief. Remimazolam, a benzodiazepine receptor agonist recognized for its anxiolytic effects, has emerged as a potential agent in managing BCP. This study explores the analgesic properties of remimazolam and its interaction with the translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, in spinal astrocytes. In the context of BCP, previous research has indicated that TSPO expression in spinal astrocytes may serve a protective regulatory function in neuropathic pain models. Building on this, the BCP mice received various doses of remimazolam on the 15th day post-inoculation, and pain behavior was assessed over time. The results showed that BCP induced an upregulation of TSPO and astrocyte activation in the spinal dorsal horn, alongside increased extracellular signal-regulated kinase (ERK) signaling and inflammatory cytokine expression. Remimazolam administration resulted in a dose-dependent reduction of pain behaviors, which corresponded with a decrease in both ERK pathway activation and inflammatory factor expression. This suggests that remimazolam's analgesic effects are mediated through its action as a TSPO agonist, leading to the attenuation of neuroinflammation and pain signaling pathways. Importantly, the analgesic effects of remimazolam were reversed by the TSPO antagonist PK11195, underscoring the pivotal role of TSPO in the drug's mechanism of action. This reversal also reinstated the heightened levels of ERK activity and inflammatory mediators, further confirming the involvement of TSPO in the modulation of these pain-related processes. These findings open new avenues for the therapeutic management of bone cancer pain, positioning remimazolam as a promising candidate for further investigation and development., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The manipulation of cell surface receptors' activity will open a new frontier for drug development and disease treatment. However, limited by the desensitization of drugs, effective physical intervention strategy remains challenging. Here, the controllable internalization of transient receptor potential vanilloid 1 (TRPV1) on neural cells by local piezoelectric field is reported. Single-cell-level local electric field is construct by synthesizing piezoelectric BiOIO 3 nanosheets (BIONSs). Upon a mild ultrasound of 0.08 W cm -2 , an electric field of 15.29 µV is generated on the surface of BIONSs, further inducing TRPV1 internalization in 5 min. The as-downregulated TRPV1 expression results in the reduction of Ca 2+ signal in a spinal neuron and the inhibition of the activity of wide range dynamic neurons, therefore effectively preventing the transmission of cancer-induced bone pain (CIBP). This strategy not only charts a new course for CIBP alleviation, but also introduces a promising nanotechnology for regulating cell surface receptors, showing significant potential in neuropathological and receptor-related diseases., (© 2024 Wiley‐VCH GmbH.)

The dorsal root ganglion (DRG) is the primary neuron responsible for transmitting peripheral pain signals to the central nervous system and plays a crucial role in pain transduction. Modulation of DRG excitability is considered a viable approach for pain management. Neuronal excitability is intricately linked to the ion channels on the neurons. The small and medium-sized DRG neurons are chiefly engaged in pain conduction and have high levels of TTX-S sodium channels, with Nav1.7 accounting for approximately 80% of the current. Voltage-gated sodium channel (VGSC or Nav) blockers are vital targets for the management of central nervous system diseases, particularly chronic pain. VGSCs play a key role in controlling cellular excitability. Clinical research has shown that Nav1.7 plays a crucial role in pain sensation, and there is strong genetic evidence linking Nav1.7 and its encoding gene SCN9A gene to painful disorders in humans. Many studies have shown that Nav1.7 plays an important role in pain management. The role of Nav1.7 in pain signaling pathways makes it an attractive target for the potential development of new pain drugs. Meanwhile, understanding the architecture of Nav1.7 may help to develop the next generation of painkillers. This review provides updates on the recently reported molecular inhibitors targeting the Nav1.7 pathway, summarizes their structure-activity relationships (SARs), and discusses their therapeutic effects on painful diseases. Pharmaceutical chemists are working to improve the therapeutic index of Nav1.7 inhibitors, achieve better analgesic effects, and reduce side effects. We hope that this review will contribute to the development of novel Nav1.7 inhibitors as potential drugs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Bone cancer pain (BCP) profoundly impacts patient's quality of life, demanding more effective pain management strategies. The aim of this systematic review was to investigate the role of inflammatory cytokines as potential molecular targets in BCP. A systematic search for animal rodent models of bone cancer pain studies was conducted in PubMed, Scopus, and Web of Science. Methodological quality and risk of bias were assessed using the SYRCLE RoB tool. Twenty-five articles met the inclusion criteria, comprising animal studies investigating molecular targets related to inflammatory cytokines in BCP. A low to moderate risk of bias was reported. Key findings in 23 manuscripts revealed upregulated classic pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-17, IL-18, IL-33) and chemokines in the spinal cord, periaqueductal gray, and dorsal root ganglia. Interventions targeting these cytokines consistently mitigated pain behaviors. Additionally, it was demonstrated that glial cells, due to their involvement in the release of inflammatory cytokines, emerged as significant contributors to BCP. This systematic review underscores the significance of inflammatory cytokines as potential molecular targets for alleviating BCP. It emphasizes the promise of targeted interventions and advocates for further research to translate these findings into effective therapeutic strategies. Ultimately, this approach holds the potential to enhance the patient's quality of life., (© 2024. The Author(s).)

The management and treatment of bone cancer pain (BCP) remain significant clinical challenges, imposing substantial economic burdens on patients and society. Extensive research has demonstrated that BCP induces changes in the gene expression of peripheral sensory nerves and neurons, which play crucial roles in the onset and maintenance of BCP. However, our understanding of the epigenetic mechanisms of BCP underlying the transcriptional regulation of pro-nociceptive (such as inflammatory factors and the transient receptor potential family) and anti-nociceptive (such as potassium channels and opioid receptors) genes remains limited. This article reviews the epigenetic regulatory mechanisms in BCP, analyzing the roles of histone modifications, DNA methylation, and noncoding RNAs (ncRNAs) in the expression of pro-nociceptive and anti-nociceptive genes. Finally, we provide a comprehensive view of the functional mechanisms of epigenetic regulation in BCP and explore the potential of these epigenetic molecules as therapeutic targets for BCP., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Bone cancer pain (BCP) represents a prevalent symptom among cancer patients with bone metastases, yet its underlying mechanisms remain elusive. This study investigated the transcriptional regulation mechanism of Kv7(KCNQ)/M potassium channels in DRG neurons and its involvement in the development of BCP in rats. We show that HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes, which encode Kv7(KCNQ)/M potassium channels in dorsal root ganglion (DRG), contributes to the sensitization of DRG neurons and the pathogenesis of BCP in rats. Also, HDAC2 requires the formation of a corepressor complex with MeCP2 and Sin3A to execute transcriptional regulation of kcnq2/kcnq3 genes. Moreover, EREG is identified as an upstream signal molecule for HDAC2-mediated kcnq2/kcnq3 genes transcription repression. Activation of EREG/EGFR-ERK-Runx1 signaling, followed by the induction of HDAC2-mediated transcriptional repression of kcnq2/kcnq3 genes in DRG neurons, leads to neuronal hyperexcitability and pain hypersensitivity in tumor-bearing rats. Consequently, the activation of EREG/EGFR-ERK-Runx1 signaling, along with the subsequent transcriptional repression of kcnq2/kcnq3 genes by HDAC2 in DRG neurons, underlies the sensitization of DRG neurons and the pathogenesis of BCP in rats. These findings uncover a potentially targetable mechanism contributing to bone metastasis-associated pain in cancer patients., (© 2024. The Author(s).)

Background: The microglial activation has been implicated in cancer-induced bone pain. Recent studies have revealed that microglia mediate synaptic pruning in the central nervous system, where the cluster of differentiation 47-signal regulatory protein α (CD47-SIRPα) axis creates a "don't eat me" signal and elicits an antiphagocytic effect to protect synapses against elimination. To date, the synaptic phagocytosis in microglia has never been investigated in the murine cancer-induced bone pain model. The present experiments sought to explore whether microglia phagocytize synapses in mice with bone cancer pain as well as the possible mechanisms., Methods: Male C3H/HeN mice were used to induce bone cancer pain. Minocycline and S-ketamine were injected into D14. The number of spontaneous flinches (NSF) and paw withdrawal mechanical thresholds (PWMT) were measured on D0, D4, D7, D10, D14, D21, and D28. Hematoxylin and eosin staining presented bone lesions. Western blotting examined the Gephyrin, CD47, and SIRPα expression. Flow cytometry evaluated the proportion of SIRPα + cells in the spine. Immunofluorescence and 3-dimensional reconstruction showed the Gephyrin puncta inside microglial lysosomes., Results: Mice embedded with tumor cells induced persistent spontaneous pain and mechanical hyperalgesia. Hematoxylin and eosin staining revealed bone destruction and tumor infiltration in marrow cavities. Microglia underwent a responsive and proliferative burst (t = -16.831, P < .001). Western blotting manifested lowered Gephyrin expression in the tumor group (D4, D7, D10, D14, D21, and D28: P < .001). Immunofluorescence and 3-dimensional reconstruction showed larger volumes of Gephyrin puncta inside microglial lysosomes (t = -23.273, P < .001; t = -27.997, P < .001). Treatment with minocycline or S-ketamine exhibited pain relief and antiphagocytic effects (t = -6.191, P < .001, t = -7.083, P < .001; t = -20.767, P < .001, t = -17.080, P < .001; t = 11.789, P < .001, t = 16.777, P < .001; t = 8.868, P < .001, t = 21.319, P < .001). Last but not least, the levels of CD47 and SIRPα proteins were downregulated (D10: P = .004, D14, D21, and D28: P < .001; D10, D14, D21, and D28: P < .001). Flow cytometry and immunofluorescence substantiated reduced microglial SIRPα (t = 11.311, P < .001; t = 12.189, P < .001)., Conclusions: Microglia-mediated GABAergic synapse pruning in the spinal cord dorsal horn in bone cancer pain mice, which might be associated with the declined CD47-SIRPα signal. Our research uncovered an innovative mechanism that highlighted microglia-mediated synaptic phagocytosis in a murine cancer-induced bone pain model., Competing Interests: The authors declared no conflicts of interest., (Copyright © 2024 International Anesthesia Research Society.)

Objectives: To observe the effect of electroacupuncture (EA) of "Zusanli" (ST36) and "Sanyinjiao" (SP6) on cancer pain and concomitant negative emotion in cancer pain model mice, and to explore its molecular mechanisms in the basolateral amygdala (BLA) by using transcriptomics techniques., Methods: C57BL/6 mice were randomized into sham operation, model and EA groups, with 10 mice in each group. The cancer pain model was established by injecting PBS suspension containing Lewis lung cancer cells into the femur. The mice in the EA group received EA stimulation(1 mA, 2 Hz) on ST36 and SP6 from the 10 th day after modeling, 20 min per day for 12 successive days. The bone damage of the distal femur was observed with X-ray and H.E. staining, respectively. The mechanical pain threshold (MPT) was detected by using von Frey. The depression-like behavior was detected by using sucrose-preference test (sucrose preference index in 12 h), and the immobility (feeling of despair) duration of forced swimming within 4 min. The BLA tissue was extracted for RNA sequencing (RNA library construction, and screening differential gene profiling by transcriptomic sequencing) and bioinformatics analysis. The real-time PCR was used to validate the mRNA expression of differentially expressed genes：tumor necrosis factor superfamily 8 (Tnfsf8), bone marrow stromal cell antigen 1 (Bst1), prodynorphin (Pdyn) and voltage-gated sodium channelβ4 (Scn4b)., Results: H.E. staining and X-ray showed significant bone damage in the distal femur in cancer pain mice. In contrast to the sham operation group, the MPT on the 1 st , 4 th , 7 th , 10 th , 14 th and 21 st day after modeling and sucrose preference index were significantly decreased ( P <0.001, P <0.000 1), and the immobility time of the forced swimming was considerably increased in the model group ( P <0.001). In contrast to the model group, the MPT values on the 14 th and 21 st day and sucrose preference index were obviously increased ( P <0.000 1, P <0.05), and the immobility time was strikingly decreased in the EA group ( P <0.01). RNA sequencing showed that a total of 404 differentially expressed genes (205 up-regulated, 199 down-regulated) were screened in the model group compared with the sham operation group, and a total of 329 differentially expressed genes (206 up-regulated and 123 down-regulated) were screened in the EA group compared with the model group. Venn diagram analysis of the differentially expressed genes showed that 45 up-regulated and 28 down-regulated genes in the model group were completely reversed by EA. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of the screened differentially expressed genes revealed that the above differential genes were mainly enriched in the ligand receptor activity, cytokine receptor binding, and cytokine activity related to neuro-inflammation, as well as in neuropeptide signaling pathways related to neuronal excitability, and calcium ion mediated signal transduction. The analysis of KEGG pathway showed that the differentially expressed genes were mainly enriched in the inflammation-related pathways, such as interleukin-17 pathway. Validation analysis of the differentially expressed genes showed that the expression levels of Tnfsf8 and Bst1 were significantly up-regulated in the model group compared with the sham operation group ( P <0.01, P <0.05), and down-regulated by EA ( P <0.01, P <0.05), while the expression levels of Pdyn and Scn4b were down-regulated in the model group in comparison with the sham operation group ( P <0.01), and up-regulated by EA ( P <0.05, P <0.01), which was consistent with the changing trend of the gene sequencing results., Conclusions: Acupuncture of ST36 and SP6 can significantly relieve cancer pain and concomitant negative emotion in cancer pain mice, which may be related to its functions in alleviating neuro-inflammation and relieving the abnormal activities of specific neurons in the BLA.

The autonomic nerve system (ANS) innervates organs and tissues throughout the body and maintains functional balance among various systems. Further investigations have shown that excessive activation of ANS not only causes disruption of homeostasis, but also may promote tumor formation. In addition, the dynamic interaction between nerve and tumor cells in the tumor microenvironment also regulate tumor progression. On the one hand, nerves are passively invaded by tumor cells, that is, perineural invasion (PNI). On the other hand, compared with normal tissues, tumor tissues are subject to more abundant innervation, and nerves can influence tumor progression through regulating tumor proliferation, metastasis and drug resistance. A large number of studies have shown that nerve-tumor crosstalk, including PNI and innervation, is closely related to the prognosis of patients, and contributes to the formation of cancer pain, which significantly deteriorates the quality of life for patients. These findings suggest that nerve-tumor crosstalk represents a potential target for anti-tumor therapies and the management of cancer pain in the future. In this review, we systematically describe the mechanism by which nerve-tumor crosstalk regulates tumorigenesis and progression., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Background: The metastasis of tumors into bone tissue typically leads to intractable pain that is both very disabling and particularly difficult to manage. We investigated here whether riluzole could have beneficial effects for the treatment of prostate cancer-induced bone pain and how it could influence the development of bone metastasis., Methods: We used a bone pain model induced by intratibial injection of human PC3 prostate cancer cells into male SCID mice treated or not with riluzole administered in drinking water. We also used riluzole in vitro to assess its possible effect on PC3 cell viability and functionality, using patch-clamp., Results: Riluzole had a significant preventive effect on both evoked and spontaneous pain involving the TREK-1 potassium channel. Riluzole did not interfere with PC3-induced bone loss or bone remodeling in vivo. It also significantly decreased PC3 cell viability in vitro. The antiproliferative effect of riluzole is correlated with a TREK-1-dependent membrane hyperpolarization in these cells., Conclusion: The present data suggest that riluzole could be very useful to manage evoked and spontaneous hypersensitivity in cancer-induced bone pain and has no significant adverse effect on cancer progression., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Conflict of interest statement The authors have declared that no conflict of interest exists., (Copyright © 2024 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Background: The underlying mechanism of chronic pain involves the plasticity in synaptic receptors and neurotransmitters. This study aimed to investigate potential roles of Neuroligins (NLs) within the spinal dorsal horn of rats in a newly established Bone Cancer Pain (BCP) model. The objective was to explore the mechanism of neuroligin involved in the occurrence and development of bone cancer pain., Methods: Using our rat BCP model, we assessed pain hypersensitivity over time. Quantitative real-time polymerase chain reaction and Western blot analysis were performed to investigate NL expression, and NLs were overexpressed in the rat spinal cord using lentiviral vectors. Immunofluorescence staining and whole-cell patch-clamp recordings were deployed to investigate the role of NLs in the development of BCP., Results: We observed reduced expression levels of NL1 and NL2, but not of NL3, within the rat spinal cord, which were found to be associated with and essential for the development of BCP in our model. Accordingly, NL1 or NL2 overexpression in the spinal cord alleviated mechanical hypersensitivity of rats. Electrophysiological experiments indicated that NL1 and NL2 are involved in BCP via regulating γ-aminobutyric acid-ergic interneuronal synapses and the activity of glutamatergic interneuronal synapses, respectively., Conclusions: Our observations unravel the role of NLs in cancer-related chronic pain and further suggest that inhibitory mechanisms are central features of BCP in the spinal dorsal horn. These results provide a new perspective and basis for subsequent studies elucidating the onset and progression of BCP., Competing Interests: Conflicts of interest The authors declare no conflicts of interest., (Copyright © 2023 Sociedade Brasileira de Anestesiologia. Published by Elsevier España S.L.U. All rights reserved.)

Bone cancer pain (BCP), due to cancer bone metastasis and bone destruction, is a common symptom of tumors, including breast, prostate, and lung tumors. Patients often experience severe pain without effective treatment. Here, using a mouse model of bone cancer, we report that MOTS-c, a novel mitochondrial-derived peptide, confers remarkable protection against cancer pain and bone destruction. Briefly, we find that the plasma level of endogenous MOTS-c is significantly lower in the BCP group than in the sham group. Accordingly, intraperitoneal administration of MOTS-c robustly attenuates bone cancer-induced pain. These effects are blocked by compound C, an AMPK inhibitor. Furthermore, MOTS-c treatment significantly enhances AMPKα 1/2 phosphorylation. Interestingly, mechanical studies indicate that at the spinal cord level, MOTS-c relieves pain by restoring mitochondrial biogenesis, suppressing microglial activation, and decreasing the production of inflammatory factors, which directly contribute to neuronal modulation. However, in the periphery, MOTS-c protects against local bone destruction by modulating osteoclast and immune cell function in the tumor microenvironment, providing long-term relief from cancer pain. Additionally, we find that chronic administration of MOTS-c has little effect on liver, renal, lipid or cardiac function in mice. In conclusion, MOTS-c improves BCP through peripheral and central synergistic effects on nociceptors, immune cells, and osteoclasts, providing a pharmacological and biological rationale for the development of mitochondrial peptide-based therapeutic agents for cancer-induced pain.

The management and therapy of bone cancer pain (BCP) remain formidable clinical challenges. Curcumin and its analogues have been shown to have anti-inflammatory and analgesic properties. In the present study, we investigated the efficacy of curcumin analogue NL04 (NL04) in modulating inflammation in spinal dorsal horn (SDH), thereby exploring its potential to reduce central sensitization of BCP in a rat model. Differing doses of NL04 and curcumin were administered intrathecally either once (on day 12 of BCP) or over seven consecutive days (from day 6-12 of BCP). Results indicated that the ED50 for NL04 and curcumin ameliorating BCP-induced mechanical hyperalgesia is 49.08 μg/kg and 489.6 μg/kg, respectively. The analgesic effects at various doses of NL04 lasted between 4 and 8 h, with sustained administration over a week maintaining pain relief for 1-4 days, while also ameliorating locomotor gait via gait analysis and reducing depressive and anxiety-like behaviors via open-field and light-dark transition tests. The analgesic effects at various doses of curcumin lasted 4 h, with sustained administration over a week maintaining pain relief for 0-2 days. ELISA, Western blotting, qPCR, and immunofluorescence assays substantiated that intrathecal administration of NL04 on days 6-12 of BCP dose-dependently lowered spinal IL-1β and IL-18 levels and significantly reduced the expression of IKKβ genes and proteins, as well as the downstream cleavage of the trans-Golgi network (TGN). Whole-cell patch-clamp results demonstrated that NL04 inhibits potassium ion efflux in rat primary spinal neurons. Thus, NL04 exhibits significant analgesic effects in a BCP rat model by downregulating IKKβ expression and inhibiting neuronal potassium ion efflux, which, in turn, suppresses the activation of NLRP3 inflammasomes and reduces IL-1β production, potentially ameliorating pain management in BCP., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Purpose: This investigation aims to explore the protective role of Naringenin (Nar) in bone cancer pain (BCP) via TNF-α-mediated NF-κB/uPA/PAR2 pathway., Methods: BCP model was manipulated by the injection of LL2 cells into femur of mice. The levels of TNF-α and uPA in bone tissue and serum were studied by ELISA. The expressions of PAR2, PKC-γ, PKA and TRPV1 were determined by qPCR and western blot. Levels of p-IKKβ, IKKβ, p-p65, p65 were determined by western blot. Levels of p-p65 and uPA in bone tissue were studied by immunohistochemistry. Behavior tests in this investigation included paw withdrawal latency (PWL) and the paw withdrawal threshold (PWT). Radiological analysis and micro-CT were used to study bone structure. The lesions of bone tissue were determined by HE staining. The Dorsal root ganglia (DRG) isolated from mice were used to determine the level of PAR2 pathway., Results: Naringenin improved the BCP-induced bone damage based on the increases of BV/TV, Conn. D, BMD and BMC and the decrease of bone destruction score. Naringenin repressed the reductions of PWT and PWL in BCP mice. Naringenin decreased the levels of PAR2, PKC-γ, PKA and TRPV1 of DRG and reduced the levels of p-IKKβ, p-p65, and uPA in serum and bone tissue in BCP. Importantly, naringenin suppressed the enhancement of TNF-α in serum and bone tissue in BCP mice., Conclusion: Naringenin alleviated pain sensitization and bone damage of mice with BCP via TNF-α-mediated NF-κB/uPA/PAR2 pathway. We demonstrated a novel pathway for anti-BCP treatment with naringenin., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background/aim: Cancer-induced bone pain (CIBP) is one of the most common symptoms of bone metastasis of tumor cells. The hypothalamus may play a pivotal role in the regulation of CIBP. However, little is known about the exact mechanisms., Materials and Methods: First, we established a CIBP model to explore the relationship among hypothalamic ghrelin, NPY and CIBP. Then, we exogenously administered NPY and NPY receptor antagonists to investigate whether hypothalamic NPY exerted an antinociceptive effect through binding to NPY receptors. Finally, we exogenously administered ghrelin to investigate whether ghrelin alleviated CIBP by inducing the production of hypothalamic NPY through the AMPK-mTOR pathway. Body weight, food intake and behavioral indicators of CIBP were measured every 3 days. Hypothalamic ghrelin, NPY and the AMPK-mTOR pathway were also measured., Results: The expression of hypothalamic ghrelin and NPY was simultaneously decreased in cancer-bearing rats, which was accompanied by CIBP. Intracerebroventricular (i.c.v.) administration of NPY significantly alleviated CIBP in the short term. The antinociceptive effect of NPY was reversed with the i.c.v. administration of the Y1R and Y2R antagonists. The administration of ghrelin activated the AMPK-mTOR pathway and induced hypothalamic NPY production to alleviate CIBP. This effect of ghrelin on NPY and antinociception was reversed with the administration of a GHS-R1α antagonist., Conclusion: Ghrelin could induce the production of hypothalamic NPY through the AMPK-mTOR pathway to alleviate CIBP, which can provide a novel therapeutic mechanism for CIBP., (Copyright © 2024, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Bone cancer pain (BCP) is refractory to currently used analgesics. Recently, sirtuin 2 (SIRT2) was reported to play a vital role in neuropathic pain but its role in BCP remains unknown. It was hypothesized that spinal SIRT2 attenuates BCP by deacetylating FoxO3a and suppressing oxidative stress. The mouse model of BCP established by injecting tumor cells into the intramedullary space of the femur demonstrated that spinal SIRT2 and FoxO3a were downregulated in BCP development. Intrathecal administration of LV-SIRT2 reduced pain hypersensitivity (mechanical and thermal nociception) in BCP mice. Spinal SIRT2 overexpression upregulated FoxO3a and antioxidant genes (SOD2 and catalase) and inhibited FoxO3a acetylation, phosphorylation, and ubiquitination. Moreover, intrathecal administration of SIRT2 shRNA induced pain hypersensitivity in normal mice. Spinal SIRT2 knockdown downregulated FoxO3a and antioxidant genes and increased FoxO3a acetylation, phosphorylation, and ubiquitination. In summary, spinal SIRT2 increases FoxO3a expression in BCP mice and inhibits oxidative stress by deacetylating FoxO3a and further reducing FoxO3a phosphorylation, ubiquitination, and degradation, leading to BCP relief., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024. Published by Elsevier B.V.)

Pain and depression comorbidity affects patients' physical and mental health, as well as quality of life. Comorbid depressive symptoms in cancer pain have a severe impact on the recognition and treatment of pain. Similarly, cancer pain patients with depression are inclined towards more despair and greater impairment. The mechanisms responsible for the comorbid depressive symptoms in bone cancer pain (BCP) have not been fully delineated. Here, it was reported that the implantation of carcinoma cells into the femoral cavity of mice led to the upregulation of major histocompatibility complex class I (MHC-I) in the hippocampus. This was associated with the activation of microglial signaling pathway mediated by the triggering receptor expressed on myeloid cells 2 protein (TREM2) and DNAX-activating protein of 12 kDa (DAP12). Pain and depression-like behaviors were reversed by the knockdown of hippocampal MHC-I via a lentiviral vector harboring ribonucleic acid interference (RNAi) sequence. Moreover, MHC-I knockdown exhibited a marked reduction in the expression of TREM2 and DAP12. These results suggested that hippocampal MHC-I was involved in BCP and depression comorbidity via upregulating the signals mediated by TREM2/DAP12 in microglia. The suppression of MHC-I could be a potential therapeutic target for BCP., Competing Interests: Declaration of Competing Interest All authors have declared that no conflict of interests exists., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Effective prevention and treatment options for bone cancer-related pain (BCP) are lacking. In recent years, numerous studies have investigated the association between m6A epigenetic modifications and pain, revealing their significant role in pain initiation and maintenance. This study aimed to provide theoretical support for the treatment of BCP and to identify target drugs for future development. Specifically, we investigated the involvement of fat mass and obesity-related protein (FTO) in rat models of BCP by administering varying doses (1/5/10 mg/kg) of the FTO inhibitor meclofenamic acid (MA) and assessing changes in mechanical sensitivity through domain analysis, gait analysis, and open-field experiments. After successfully establishing the BCP model, we verified it by performing mechanical sensitivity assessments. We observed significantly increased expression levels of the demethylase FTO within the spinal dorsal horn accompanied by decreased m6A methylation levels in the model. Compared with untreated BCP rats, remarkably improved behavioral responses indicative of reduced pain were observed in the model rats after administration of 10 mg/kg MA, concomitant with decreased expression levels of FTO and increased m6A methylation levels. Compared with untreated BCP rats, the expression levels of p-ERK and pro-inflammatory cytokines were also significantly decreased after MA administration. Taken together, FTO can downregulate m6A methylation level and activate ERK/inflammatory cytokines signaling pathway to maintain BCP in rats., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Cancer‑induced bone pain (CIBP) is characterized as moderate to severe pain that negatively affects the daily functional status and quality of life of patients. When cancer cells metastasize and grow in bone marrow, this activates neuroinflammation in the spinal cord, which plays a vital role in the generation and persistence of chronic pain. In the present study, a model of CIBP was constructed by inoculating of MRMT‑1 rat breast carcinoma cells into the medullary cavity of the tibia in male Sprague‑Dawley rats. Following two weeks of surgery, CIBP rats exhibited damaged bone structure, increased pain sensitivity and impaired motor coordination. Neuroinflammation was activated in the spinal cords of CIBP rats, presenting with extensive leukocyte filtration, upregulated cytokine levels and activated astrocytes. Histone deacetylase 6 (HDAC6) works as a therapeutic target for chronic pain. The intrathecal injection of the HDAC6 inhibitor tubastatin A (TSA) in the lumbar spinal cord resulted in decreased spinal inflammatory cytokine production, suppressed spinal astrocytes activation and reduced NOD‑like receptor pyrin domain containing 3 (NLRP3) inflammasome activity. Consequently, this effect alleviated spontaneous pain and mechanical hyperalgesia and recovered motor coordination in CIBP rats. It was demonstrated by immunoprecipitation assay that TSA treatment reduced the interaction between HDAC6 and NLRP3. Cell research on C6 rat glioma cells served to verify that TSA treatment reduced HDAC6 and NLRP3 expression. In summary, the findings of present study indicated that TSA treatment alleviated cancer‑induced bone pain through the inhibition of HDAC6/NLRP3 inflammasome signaling in the spinal cord.

Pain is a major symptom in cancer patients, and cancer-induced bone pain (CIBP) is the most common type of moderate and severe cancer-related pain. The current available analgesic treatments for CIBP have adverse effects as well as limited therapeutic effects. Acupuncture is proved effective in pain management as a safe alternative therapy. We evaluated the analgesic effect of acupuncture in treatment of cancer pain and try to explore the underlying analgesic mechanisms. Nude mice were inoculated with cancer cells into the left distal femur to establish cancer pain model. Electroacupuncture (EA) treatment was applied for the xenograft animals. Pain behaviors of mice were evaluated, followed by the detections of neuropeptide-related and inflammation-related indicators in peripheral and central levels. EA treatment alleviated cancer-induced pain behaviors covering mechanical allodynia, thermal hyperalgesia and spontaneous pain, and also down-regulated immunofluorescence expressions of neuropeptide CGRP and p75 in the skin of affected plantar area in xenograft mice, and inhibited expressions of overexpressed neuropeptide-related and inflammation-related protein in the lumbar spinal cord of xenograft mice. Overall, our findings suggest that EA treatment ameliorated cancer-induced pain behaviors in the mouse xenograft model of cancer pain, possibly through inhibiting the expressions of neuropeptide-related and inflammation-related protein in central level following tumor cell xenografts., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Cancer-induced bone pain (CIBP) is one of the most common and feared symptoms in patients with advanced tumors. The X-C motif chemokine ligand 12 (CXCL12) and the CXCR4 receptor have been associated with glial cell activation in bone cancer pain. Moreover, mitogen-activated protein kinases (MAPKs), as downstream CXCL12/CXCR4 signals, and c-Jun, as activator protein AP-1 components, contribute to the development of various types of pain. However, the specific CIBP mechanisms remain unknown. Esketamine is a non-selective N-methyl-d-aspartic acid receptor (NMDA) inhibitor commonly used as an analgesic in the clinic, but its analgesic mechanism in bone cancer pain remains unclear. We used a tumor cell implantation (TCI) model and explored that CXCL12/CXCR4, p-MAPKs, and p-c-Jun were stably up-regulated in the spinal cord. Immunofluorescence images showed activated microglia in the spinal cord on day 14 after TCI and co-expression of CXCL12/CXCR4, p-MAPKs (p-JNK, p-ERK, p-p38 MAPK), and p-c-Jun in microglia. Intrathecal injection of the CXCR4 inhibitor AMD3100 reduced JNK and c-Jun phosphorylations, and intrathecal injection of the JNK inhibitor SP600125 and esketamine also alleviated TCI-induced pain and reduced the expression of p-JNK and p-c-Jun in microglia. Overall, our data suggest that the CXCL12/CXCR4-JNK-c-Jun signaling pathway of microglia in the spinal cord mediates neuronal sensitization and pain hypersensitivity in cancer-induced bone pain and that esketamine exerts its analgesic effect by inhibiting the JNK-c-Jun pathway., Competing Interests: Declaration of conflicting interestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: Schematic overview plotted by Figdraw. The authors declare that the study was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Objective: This study aimed to clarify the interactions between the tongue and primary afferent fibers in tongue cancer pain., Methods: A pharmacological analysis was conducted to evaluate mechanical hypersensitivity of the tongues of rats with squamous cell carcinoma (SCC). Changes in trigeminal ganglion (TG) neurons projecting to the tongue were analyzed using immunohistochemistry and western blotting., Results: SCC inoculation of the tongue caused persistent mechanical sensitization and tumor formation. Trypsin expression was significantly upregulated in cancer lesions. Continuous trypsin inhibition or protease-activated receptor 2 (PAR2) antagonism in the tongue significantly inhibited SCC-induced mechanical sensitization. No changes were observed in PAR2 and transient receptor potential vanilloid 4 (TRPV4) levels in the TG or the number of PAR2-and TRPV4-expressing TG neurons after SCC inoculation. In contrast, the relative amount of phosphorylated TRPV4 in the TG was significantly increased after SCC inoculation and abrogated by PAR2 antagonism in the tongue. TRPV4 antagonism in the tongue significantly ameliorated the mechanical sensitization caused by SCC inoculation., Conclusions: Our findings indicate that tumor-derived trypsin sensitizes primary afferent fibers by PAR2 stimulation and subsequent TRPV4 phosphorylation, resulting in severe tongue pain., Competing Interests: Declaration of Competing Interest The authors declare that they have no competing interests., (Copyright © 2023 Japanese Association for Oral Biology. Published by Elsevier B.V. All rights reserved.)

Due to its complex pathological mechanisms, bone cancer pain (BCP) has become an increasingly challenging clinical issue, there is an urgent need to identify the underlying mechanisms of BCP. In our present study, we found that decreased expression of miR-199a-3p in spinal dorsal horn (SDH) neurons contributed to BCP hypersensitivity. Intrathecal administration of miR-199a-3p agomir alleviated the initiation of tumor inoculation induced pain hypersensitivity and suppressed the expression of DNMT3A. Subsequently, luciferase assays confirmed direct binding between miR-199a-3p and Dnmt3a mRNA. AAV-DNMT3A-shRNA microinjection relieved mechanical hyperalgesia and upregulated the expression of Nrf2 levels in BCP. In naïve rats, Overexpression of DNMT3A yielded the opposite effects. Finally, increase of DNMT3A by lentiviral vector abolished miR-199a-3p-mediated alleviation hypersensitivity effects on BCP progression. Taken these together, our findings highlighted a novel contribution of miR-199a-3p to BCP and provided a fresh outlook on potential mechanism research for BCP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Pathological pain presents significant challenges in clinical practice and research. Aquaporin-4 (AQP4), which is primarily found in astrocytes, is being considered as a prospective modulator of pathological pain. This review examines the association between AQP4 and pain-related diseases, including cancer pain, neuropathic pain, and inflammatory pain. In cancer pain, upregulated AQP4 expression in tumor cells is linked to increased pain severity, potentially through tumor-induced inflammation and edema. Targeting AQP4 may offer therapeutic strategies for managing cancer pain. AQP4 has also been found to play a role in nerve damage. Changes in AQP4 expression have been detected in pain-related regions of the brain and spinal cord; thus, modulating AQP4 expression or function may provide new avenues for treating neuropathic pain. Of note, AQP4-deficient mice exhibit reduced chronic pain responses, suggesting potential involvement of AQP4 in chronic pain modulation, and AQP4 is involved in pain modulation during inflammation, so understanding AQP4-mediated pain modulation may lead to novel anti-inflammatory and analgesic therapies. Recent advancements in magnetic resonance imaging (MRI) techniques enable assessment of AQP4 expression and localization, contributing to our understanding of its involvement in brain edema and clearance pathways related to pathological pain. Furthermore, targeting AQP4 through gene therapies and small-molecule modulators shows promise as a potential therapeutic intervention. Future research should focus on utilizing advanced MRI techniques to observe glymphatic system changes and the exchange of cerebrospinal fluid and interstitial fluid. Additionally, investigating the regulation of AQP4 by non-coding RNAs and exploring novel small-molecule medicines are important directions for future research. This review shed light on AQP4-based innovative therapeutic strategies for the treatment of pathological pain. Dark blue cells represent astrocytes, green cells represent microglia, and red ones represent brain microvasculature., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Drive from peripheral neurons is essential in almost all pain states, but pharmacological silencing of these neurons to effect analgesia has proved problematic. Reversible gene therapy using long-lived chemogenetic approaches is an appealing option. We used the genetically activated chloride channel PSAM 4 -GlyR to examine pain pathways in mice. Using recombinant AAV9-based delivery to sensory neurons, we found a reversal of acute pain behavior and diminished neuronal activity using in vitro and in vivo GCaMP imaging on activation of PSAM 4 -GlyR with varenicline. A significant reduction in inflammatory heat hyperalgesia and oxaliplatin-induced cold allodynia was also observed. Importantly, there was no impairment of motor coordination, but innocuous von Frey sensation was inhibited. We generated a transgenic mouse that expresses a CAG-driven FLExed PSAM 4 -GlyR downstream of the Rosa26 locus that requires Cre recombinase to enable the expression of PSAM 4 -GlyR and tdTomato. We used Na V 1.8 Cre to examine the role of predominantly nociceptive Na V 1.8+ neurons in cancer-induced bone pain (CIBP) and neuropathic pain caused by chronic constriction injury (CCI). Varenicline activation of PSAM 4 -GlyR in Na V 1.8-positive neurons reversed CCI-driven mechanical, thermal, and cold sensitivity. Additionally, varenicline treatment of mice with CIBP expressing PSAM 4 -GlyR in Na V 1.8+ sensory neurons reversed cancer pain as assessed by weight-bearing. Moreover, when these mice were subjected to acute pain assays, an elevation in withdrawal thresholds to noxious mechanical and thermal stimuli was detected, but innocuous mechanical sensations remained unaffected. These studies confirm the utility of PSAM 4 -GlyR chemogenetic silencing in chronic pain states for mechanistic analysis and potential future therapeutic use., Competing Interests: The authors declare no competing financial interests., (Copyright © 2023 Haroun et al.)

Bone cancer pain (BCP) is one of the most prevalent and serious symptoms of patients with cancer. Currently, the medical interventions used for the treatment of BCP do not act with optimal safety and efficacy. In this study, we appraised whether the hypoxia-inducible factor 1α (HIF-1α)/metalloproteinase-9 (MMP9) axis activates the PI3K/AKT pathway, resulting in elevated spinal cord central sensitization and aggravated BCP. BCP rats were established by tibial injection of Walker 256 cells, followed by different interventions in rats using HIF-1ɑ inhibitor LW6 or antibody treatments. After treatment with LW6 or antibody against HIF-1α, central sensitization in the spinal cord tissues of rats was inhibited, and pain perception in rats was reduced. Moreover, the activation of glial cells in the spinal cord tissues was ameliorated. The expression of MMP9 was remarkably suppressed in spinal cord tissues after inhibition of HIF-1ɑ activity, and the activity of the PI3K/AKT signaling pathway was inhibited. Further activation of MMP9 expression suppressed the alleviating effect of HIF-1ɑ inhibitor LW6 or antibody on pain perception in rats inoculated with tumors. Taken together, our studies suggest a HIF-1α/MMP9-mediated activation of PI3K/AKT in the spinal cord tissues, resulting in increased pain perception in a rat model with BCP., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Bone cancer pain (BCP) remains a clinical challenge due to the limited and side effects of therapeutic methods. Folic acid has been known as an FDA approved dietary supplement and proved to have an analgesic effect in neuropathic pain. Here we investigate the role and mechanism of folic acid in bone cancer pain of a rat model., Methods: Walker 256 tumor cells were inoculated into the left tibia of rats to induce bone cancer pain model. Pain reflex were assessed by paw withdrawal threshold (PWT) response to Von Frey filaments and paw withdrawal latency (PWL) response to thermal stimulation. Folic acid was injected intraperitoneally to evaluate its analgesic effect in rats with bone cancer pain. Western blotting and qPCR were used to determine P2X2/3 receptor protein and mRNA levels in ipsilateral L4-6 dorsal root ganglion (DRG) and spinal dorsal horn (SDH)., Results: The PWT and PWL of rats with bone cancer pain were obviously decreased compared to the naïve and sham rats. Interestingly, continuous folic acid treatment significantly increased the PWT and PWL of rats with bone cancer pain. P2X2 and P2X3 receptors were clearly upregulated at both mRNA and protein expression in L4-6 DRG and SDH of rats with bone cancer pain. P2X2 and P2X3 receptors were mainly localized with CGRP (calcitonin gene-related peptide) or IB4 (isolectin B4) positive neurons in L4-6 DRG of rats with bone cancer pain. Notably, continuous folic acid treatment significantly reduced the expression of P2X2 and P2X3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Finally, intrathecal injection of A317491 (a selective antagonist of P2X2/3 receptors) markedly elevated the PWT and PWL of rats with bone cancer pain., Conclusion: These results suggest that folic acid has an effective antinociceptive effect on bone cancer pain, which is mediated by downregulating P2X2/3 receptors in L4-6 DRG and SDH of rats with bone cancer pain. Folic acid may be a novel therapeutic strategy in cancer patients for pain relief., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: This study aimed to assess the potential function of Caveolin-1 (CAV-1) in mice with bone cancer pain., Method: Using a mice bone cancer pain model we explored the contribution of CAV-1 expression to bone cancer pain on the 14th day after surgery, mice in the tumor group were randomized and treated with increasing doses of the CAV-1 inhibitor, methyl-beta-cyclodextrin. Pain was assessed by monitoring the number of spontaneous flinches (NSF) and paw withdrawal mechanical threshold (PMWT)mechanical withdrawal threshold (MWT). The localization and expression of CAV-1 in mouse neurons was also determined. Additionally, the protein levels of CAV-1, extracellular signal regulated kinase (ERK) 1/2, cAMP response element-binding protein (CREB) were monitored in mouse spinal cord tissues by western blotting., Results: CAV-1 was remarkably upregulated in the spinal cord of the tumor group on the 4th day after surgery, then downregulated on day 10, and upregulated again at day 14. Such CAV-1 levels were maintained until day 28. In the tumor group, the expression of p-ERK1/2 and p-CERB were upregulated at day 14 after surgery. Intrathecal injection of methyl-beta-cyclodextrin (MCD) downregulated p-ERK1/2 and p-CERB expression which correlated with alleviation of pain., Conclusion: Inhibition of CAV-1 in the spinal cord alleviates bone cancer pain in mice which correlates with inhibition of the ERK/CREB pathway., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Ubiquitin-mediated degradation of the Mas-related G protein-coupled receptor C (MrgC) reduces the number of receptors. However, the specific deubiquitinating enzyme antagonize this process has not been reported. In this study, we investigated the effect of ubiquitin-specific protease-48 (USP48) on bone cancer pain (BCP) and its effect on MrgC., Methods: A mouse model of BCP was established. BCP behaviours of mice were assessed after intrathecal injection of adeno-associated virus (AAV)-USP48. USP48 and MrgC interactions were studied by immunoprecipitation. Overexpression and knockdown of USP48 were conducted in N2a cells to investigate the effect of USP48 on MrgC receptor number and ubiquitination., Results: Spinal cord level USP48 expression was reduced in mice with BCP. Intrathecal injection of AAV-USP48 increased paw withdrawal mechanical threshold and reduced spontaneous flinching in mice. In N2a cells, there were increased number of MrgC receptors after overexpression of USP48 and decreased number of MrgC receptors after knockdown of USP48. USP48 interacted with MrgC and overexpression of USP48 altered the level of ubiquitination of MrgC., Conclusion: USP48 antagonizes ubiquitin-mediated autophagic degradation of MrgC and alleviates BCP in a murine animal model. Our findings may provide a new perspective for the treatment of BCP., Significance: Our finding may provide an important theoretical basis as well as an intervention target for clinical development of drugs for BCP., (© 2023 European Pain Federation - EFIC ®.)

Upregulation of P2X3 receptor (P2X3R) has been strongly implicated in nociceptive signaling including bone cancer pain (BCP). The present study, using rat bone cancer model, aimed to explore the role of P2X3R in regulating rat pain behavior under the intervention of electroacupuncture (EA). The BCP model was successfully established by injection with MRMT-1 breast cancer cell into the medullary cavity of left tibia for 3 × 10 4 cells/3 μL PBS in rats as revealed by obvious bone destruction, decreased paw withdrawal thresholds (PWTs), and reduced paw withdrawal latencies (PWLs). Western blot analyses showed that P2X3R expression was significantly upregulated in ipsilateral lumbar 4-6 (L4-6) dorsal root ganglia (DRG), but the difference not seen in spinal cord dorsal horn (SCDH). With the in-depth study of P2X3R activation, we observed that intrathecal injection of P2X3R agonist α,β-meATP aggravated MRMT-1 induced BCP, while injection of P2X3R inhibitor A-317491 alleviated pain. Subsequently, we demonstrated that BCP induced mechanical allodynia and thermal hyperalgesia were attenuated after EA treatment. Under EA treatment, total P2X3R protein expression in ipsilateral DRGs was decreased, and it is worth mentioning that decreased expression of P2X3R membrane protein, which indicated that both the expression and membrane trafficking of P2X3R were inhibited by EA. The immunofluorescence assay showed that EA stimulation exerted functions by reducing the expression of P2X3R-positive cells in ipsilateral DRGs of BCP rats. Ca 2+ imaging analysis revealed that the EA stimulation decreased the percentage of α,β-meATP responsive neurons in DRGs and inhibited calcium influx. Notably, the inhibitory effect of EA on mechanical allodynia and nociceptive flinches was abolished by intrathecal injection of α,β-meATP. These findings demonstrated EA stimulation ameliorated mechanical allodynia and thermal hyperalgesia in rat model of MRMT-1-induced BCP. EA exerts analgesic effect on BCP by reducing the overexpression and functional activity of P2X3R in ipsilateral DRGs of BCP rats. Our work first demonstrates the critical and overall role of P2X3R in EA's analgesia against peripheral sensitization of MRMT-1-induced BCP and further supports EA as a potential therapeutic option for cancer pain in clinic., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Pain is one of the most severe complications affecting the quality of life of cancer patients. Although substantial progress has been made in the diagnosis and treatment of cancer, the neurobiological mechanism of cancer pain is still unclear. In the present study, we identified the critical role of CXC chemokine 2 (CXCL2), released by Schwann cells after being activated by cancer cells, in maintaining cancer-induced macrophage infiltration and the resulting mechanical hypersensitivity and persistent spontaneous nociception. In vitro, Schwann cells cocultured with breast cancer cells exhibited a significant increase in CXCL2 expression; in addition, conditioned medium from Schwann cells activated by breast cancer cells had a similar effect to recombinant CXCL2 in terms of inducing macrophage migration. Targeting CXCL2 signaling by both CXC chemokine receptor 2 (CXCR2) antagonist pharmacological blockade and anti-CXCL2 mAb immunological blockade robustly prevented conditioned medium-induced macrophage migration. In vivo, both application of recombinant CXCL2 and perineural breast cancer cell implantation resulted in mechanical hypersensitivity and persistent spontaneous nociception in mice, along with increased macrophage infiltration into the sciatic nerves. Similar to the in vitro results, inhibition of CXCL2/CXCR2 signaling or conditional knockdown of CXCL2 in sciatic nerve Schwann cells effectively attenuated breast cancer cell-induced mechanical hypersensitivity, persistent spontaneous nociception, and macrophage recruitment in the sciatic nerve. Mechanistically, we found that redox effector factor-1 (Ref-1) secreted by breast cancer cells activated hypoxia inducible factor-1α (HIF-1α) expression and inhibited reactive oxygen species (ROS) production in Schwann cells, ultimately inducing CXCL2 expression in Schwann cells. In brief, the present study expands new insights into cancer pain mechanisms from promising animal models to provide new strategies for the control of cancer pain., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The periaqueductal gray (PAG) is an important relay center for the descending pathways that regulate nociceptive information transduction. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels play critical roles in the nerve injury-induced pain hypersensitivity. Previous studies have identified that HCN1 and HCN2 channel protein located in the ventral-lateral periaqueductal gray (vlPAG), a region important for pain regulation. However, it is not clear whether the HCN channel in vlPAG is involved in bone cancer pain (BCP). In this study, we assessed the role of HCN channels in BCP by measuring changes of HCN channel expression and activity in vlPAG neurons in bone cancer rats. In the present study, the BCP model was established by injecting SHZ-88 breast cancer cells into the right tibia bone marrow in rats. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured to evaluate pain behavior in rats. HCN1 and HCN2 channels expression in vlPAG were detected by using Western Blot and immunohistochemistry. In addition, the cAMP level in vlPAG neurons was detected by ELISA, and HCN channel current (I h ) of vlPAG neurons was recorded by whole cell patch-clamp to evaluate HCN channel activity. As a result, decreased MWT and TWL were observed in rats on 7d after SHZ-88 cell inoculation, and the allodynia was sustained until 21d after inoculation. At the same time, HCN1 and HCN2 channels expression and neuronal I h in vlPAG were significantly increased in BCP rats. In addition, the level of cAMP in vlPAG also increased after SHZ-88 cell inoculation. Furthermore, intravlPAG injection of ZD7288 (HCN channels antagonist) could significantly reduce hyperalgesia and the elevation of cAMP in vlPAG in BCP rats. Our observations suggest that the elevation of cAMP may promote the activation of HCN channels in vlPAG in bone cancer rats, thereby promoting the development of bone cancer pain., Competing Interests: Declaration of competing interest Final approval of the version to be published: All authors. The authors declare no conflict of interest in this study., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Given that the incidence of cancer is dramatically increasing nowadays, cancer-related neuropathic pain including tumor-related and therapy-related pain gradually attracts more attention from researchers, which basically behaves as a metabolic-neuro-immune disorder with worse clinical outcomes and prognosis. Among various mechanisms of neuropathic pain, the common underlying one is the activation of inflammatory responses around the injured or affected nerve(s). Innate and adaptive immune reactions following nerve injury together contribute to the regulation of pain. On the other hand, the tumor immune microenvironment involving immune cells, as exemplified by lymphocytes, macrophages, neutrophils and dendritic cells, inflammatory mediators as well as tumor metastasis have added additional characteristics for studying the initiation and maintenance of cancer-related neuropathic pain. Of interest, these immune cells in tumor microenvironment exert potent functions in promoting neuropathic pain through different signaling pathways. To this end, this review mainly focuses on the contribution of different types of immune cells to cancer-related neuropathic pain, aims to provide a comprehensive summary of how these immune cells derived from the certain tumor microenvironment participate in the pathogenesis of neuropathic pain. Furthermore, the clarification of roles of various immune cells in different tumor immune microenvironments associated with certain cancers under neuropathic pain states constitutes innovative biology that takes the pain field in a different direction, and thereby provides more opportunities for novel approaches for the prevention and treatment of cancer-related neuropathic pain.

Background: Neuroinflammation in the peripheral nervous system has been linked to cancer metastasis-induced bone pain. The stimulator of interferon genes (STING), an innate immune sensor for cytosolic DNA, plays an important role in inflammation and cancer metastasis and is reported to be a critical regulator of nociception. Here, we examined the role of STING in primary nociceptive neurons and chronic pain to determine if it could be a new target for treating bone cancer pain (BCP)., Methods: Walker 256 cancer cells were injected intratibially to induce bone cancer pain in rats. STING and its downstream inflammatory factors in dorsal root ganglia (DRG) were detected using western blotting and immunofluorescent staining. Transmission electron microscopy and the BCL2-associated X (Bax) expression were used to detect the mitochondrial stress in DRG neurons. C-176, a specific inhibitor of STING, was used to block STING activation and to test the pain behavior., Results: Mechanical hyperalgesia and spontaneous pain were observed in BCP rats, accompanied by the upregulation of the STING expression in the ipsilateral L4-5 DRG neurons which showed significant mitochondrion stress. The STING/TANK-binding kinase 1 (TBK1)/nuclear factor-kappa B (NF-κB) pathway activation was observed in the DRGs of BCP rats as well as increased IL-1β, IL-6, and TNF-α expression. C-176 alleviated bone cancer pain and reduced the STING and its downstream inflammatory pathway., Conclusion: We provide evidence that STING pathway activation leads to neuroinflammation and peripheral sensitization. Pharmacological blockade of STING may be a promising novel strategy for preventing BCP., (© 2022. The Author(s).)

The G protein-coupled P2Y12 receptor (P2Y12R) was cloned in platelets and found to play a key role in maintaining platelet function in hemostasis and thrombosis, and these effects could be mediated by the P2Y12R. However, it has recently been found that P2Y12R-mediated the progression of tumor through interactions between platelets and tumor and stromal cells, as well as through products secreted by platelets. During tumor progression, tumor cells or other cells in the tumor microenvironment (such as immune cells) can secrete large amounts of ATP into the extracellular matrix, and extracellular ATP can be hydrolyzed into ADP. ADP is a P2Y12R activator and plays an important regulatory role in the proliferation and metastasis of tumor cells. P2Y12R is involved in platelet-cancer cell crosstalk and become a potential target for anticancer therapy. Moreover, tumor progression can induce pain, which seriously affects the quality of life of patients. P2Y12R is expressed in microglia and mediates the activities of microglial and participates in the occurrence of cancer pain. Conversely, inhibiting P2Y12R activation and down-regulating its expression has the effect of inhibiting tumor progression and pain. Therefore, P2Y12R can be a common therapeutic target for both. In this article, we explored the potential link between P2Y12R and cancer, discussed the intrinsic link of P2Y12R in cancer pain and the pharmacological properties of P2Y12R antagonists in the treatment of both., Competing Interests: Conflict of interest We confirmed that the paper has been seen and admitted by co-authors, approved the submission to the journal. We confirmed that there are no conflicts of interest in this paper. Thank you very much., (Copyright © 2022 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Bone cancer pain (BCP), which seriously affects the quality of life of patients, remains a clinically challenging problem. Hence, there is an urgent need to investigate new mechanisms and develop new therapeutics to relieve BCP. In the present study, we investigated the analgesic effect of melatonin on BCP and the underlying mechanisms. Male C57BL/6 mice were used to establish BCP models. We found that the levels of sirtuin 1 (SIRT1) and nucleus-high mobility group box-1 (HMGB1) were decreased, whilst the levels of HMGB1, cytoplasm-HMGB1 and inflammatory cytokines (TNF-α, IL-6, IL-1β) were increased in the spinal cord of BCP mice on days 7, 14 and 21 after implantation compared with the levels in sham mice. Intrathecal administration of melatonin dose-dependently increased values of PWMT and TWL compared with the BCP group. However, intrathecal administration of EX527 (a selective SIRT1 antagonist) reversed the analgesic effect of melatonin. Moreover, mice in the melatonin group exhibited an increase in SIRT1 and nucleus-HMGB1, whilst there was a decrease in HMGB1, cytoplasm-HMGB1, rage, acetyl-HMGB1 and inflammatory cytokines compared with those in BCP mice. EX527 also reversed these changes. Furthermore, SIRT1 physically interacted with HMGB1 in the BCP mice. In conclusion, intrathecal administration of melatonin attenuates BCP through SIRT1-dependent inhibition of HMGB1 translocation and inflammatory cytokines. Melatonin may be a promising drug for the clinical treatment of BCP., Competing Interests: Declaration of competing interest The authors declare no potential conflicts of interest., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: Bone cancer pain (BCP) is the most severe and intractable type of cancer pain. Emerging evidence has demonstrated that activated microglia in the spinal cord could release a series of neurotoxic substances to stimulate neurons and form neuronal sensitization. The P2X7 receptor (P2X7R) is a nonselective ATP-gated ion channel predominantly present in microglia in the spinal cord as the key modulator of microglial activity. However, the specific effect and underlying molecular mechanism of P2X7R in BCP have not yet been elucidated., Objectives: This study aimed at investigating whether P2X7R-induced BCP by regulating microglial activity through NLRP3/IL-1beta signaling involvement in BCP., Study Design: Controlled animal study., Methods: A BCP animal model was established by injecting Walker-256 breast cancer cells into the tibia of female rats. Fifty percent paw withdrawal thresholds (50% PWTs), number of spontaneous flinches (NSF), and limb use scores were used to evaluate behavior in rats. P2X7R inhibitor brilliant blue G (BBG) was used to assess the role of P2X7R in BCP-induced NLRP3 inflammasome activation. Western blot, RT-PCR, and immunofluorescence were used for quantitative comparison. In vitro, BV2 cells were treated with lipopolysaccharide (LPS) and BzATP, in the presence or absence of P2X7 siRNA, with nigericin (an agonist of the NLRP3 inflammasome) to further study the mechanism of P2X7R regulate NLRP3/IL-1beta signaling., Results: The inhibition of spinal P2X7R with BBG could effectively inhibit BCP due to suppressing the expression of NF-kappaB p-p65, NLRP3 inflammasome formation, and downstream pain factors IL-1beta. Furthermore, P2X7 siRNA could reduce microglial activity, the nuclear translocation of NF-kappaB, and the synthesis of NLRP3 and IL-1beta in BV2 cells. In addition, nigericin partially reversed the ameliorating effect of P2X7 siRNA on BV2 cells induced by LPS and BzATP., Limitations: BBG could relieve BCP but not improve the destruction of bone, which may be related to the specificity of inoculated cells. Further mechanisms should be investigated., Conclusion: These findings suggest that targeting the microglial P2X7R activated NLRP3/IL-1beta signaling pathway could serve as a potential strategy for BCP treatment.

Cancer-induced bone pain (CIBP) occurs frequently among advanced cancer patients. Voltage-gated sodium channels (VGSCs) have been associated with chronic pain, but how VGSCs function in CIBP is poorly understood. Here, we aimed to investigate the specific role of VGSCs in the dorsal root ganglia (DRGs) in CIBP. A CIBP rat model was generated by the intratibial inoculation of MRMT-1 breast carcinoma cells. Transcriptome sequencing was conducted to assess the gene expression profiles. The expression levels of key genes and differentiated genes related to activated pathways were measured by Western blotting and qPCR. We implanted a catheter intrathecally for the administration of lentivirus and drugs. Then, the changes in the mechanical withdrawal threshold (MWT) were measured. We identified 149 differentially expressed mRNAs (DEmRNAs) in the DRGs of CIBP model rats. The expression of Na v 1.6, which was among these DEmRNAs, was significantly upregulated. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the DEmRNAs showed that they were mainly enriched in the mitogen-activated protein kinase (MAPK) pathway. The decrease in MWT induced by bone cancer was attenuated by Na v 1.6 knockdown. Western blot analysis revealed that a p38 inhibitor decreased the expression of Na v 1.6 and attenuated pain behavior. Our study shows that the upregulation of Na v 1.6 expression by p38 MAPK in the DRGs of rats contributes to CIBP.

Tumor innervation is a common phenomenon with unknown mechanism. Here, we discovered a direct mechanism of tumor-associated macrophage (TAM) for promoting de novo neurogenesis via a subset showing neuronal phenotypes and pain receptor expression associated with cancer-driven nocifensive behaviors. This subset is rich in lung adenocarcinoma associated with poorer prognosis. By elucidating the transcriptome dynamics of TAM with single-cell resolution, we discovered a phenomenon "macrophage to neuron-like cell transition" (MNT) for directly promoting tumoral neurogenesis, evidenced by macrophage depletion and fate-mapping study in lung carcinoma models. Encouragingly, we detected neuronal phenotypes and activities of the bone marrow-derived MNT cells (MNTs) in vitro. Adoptive transfer of MNTs into NOD/SCID mice markedly enhanced their cancer-associated nocifensive behaviors. We identified macrophage-specific Smad3 as a pivotal regulator for promoting MNT at the genomic level; its disruption effectively blocked the tumor innervation and cancer-dependent nocifensive behaviors in vivo. Thus, MNT may represent a precision therapeutic target for cancer pain.

Oral cancer pain is attributed to the release from cancers of mediators that sensitize and activate sensory neurons. Intraplantar injection of conditioned media (CM) from human tongue cancer cell line HSC-3 or OSC-20 evokes nociceptive behavior. By contrast, CM from noncancer cell lines, DOK, and HaCaT are non-nociceptive. Pain mediators are carried by extracellular vesicles (EVs) released from cancer cells. Depletion of EVs from cancer cell line CM reverses mechanical allodynia and thermal hyperalgesia. CM from non-nociceptive cell lines become nociceptive when reconstituted with HSC-3 EVs. Two miRNAs (hsa-miR-21-5p and hsa-miR-221-3p) are identified that are present in increased abundance in EVs from HSC-3 and OSC-20 CM compared to HaCaT CM. The miRNA target genes suggest potential involvement in oral cancer pain of the toll like receptor 7 (TLR7) and 8 (TLR8) pathways, as well as signaling through interleukin 6 cytokine family signal transducer receptor (gp130, encoded by IL6ST) and colony stimulating factor receptor (G-CSFR, encoded by CSF3R), Janus kinase and signal transducer and activator of transcription 3 (JAK/STAT3). These studies confirm the recent discovery of the role of cancer EVs in pain and add to the repertoire of algesic and analgesic cancer pain mediators and pathways that contribute to oral cancer pain., (© 2022 The Authors. Advanced Biology published by Wiley-VCH GmbH.)

We investigated the neural correlates for chronic cancer pain conditions by retrospectively analyzing whole brain regions on 18F-fluoro-2-deoxyglucose-positron emission tomography images acquired from 80 patients with head and neck squamous cell carcinoma and esophageal cancer. The patients were divided into three groups according to perceived pain severity and type of analgesic treatment, namely patients not under analgesic treatment because of no or minor pain, patients with good pain control under analgesic treatment, and patients with poor pain control despite analgesic treatment. Uncontrollable cancer pain enhanced the activity of the hippocampus, amygdala, inferior temporal gyrus, and temporal pole. Metabolic connectivity analysis further showed that amygdala co-activation with the hippocampus was reduced in the group with poor pain control and preserved in the groups with no or minor pain and good pain control. The increased although imbalanced activity of the medial temporal regions may represent poor pain control in patients with cancer. The number of patients who used anxiolytics was higher in the group with poor pain control, whereas the usage rates were comparable between the other two groups. Therefore, further studies should investigate the relationship between psychological conditions and pain in patients with cancer and analyze the resultant brain activity.Trial registration: This study was registered at clinicaltrials.gov on 9/3/20 (NCT04537845)., (© 2022. The Author(s).)

Patients with bone cancer pain (BCP) are more prone to aversion. which not only causes mental distress but also aggravates BCP. However, the mechanism of BCP-related aversion is still unclear. Previous studies have demonstrated that the brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (TrkB) signaling pathway of the rostral anterior cingulate cortex (rACC) plays an important role in the regulation of emotions related to chronic pain, such as neuropathic pain or inflammatory pain; however, few studies have investigated the role of this pathway in cancer pain. This study explored the role of BDNF in cancer pain-related aversion in the rACC and to determine whether N-methyl D-aspartate receptor subtype 2B (NR2B) and extracellular signal-regulated kinase (ERK)-cAMP response element-binding (CREB) signaling are involved in cancer pain-related aversion. A Sprague-Dawley rat model of BCP (one of the classic BCP models) was established, and the changes in pain aversion were detected by mechanical stimulation-induced conditioned place avoidance. Our findings confirmed that rats with BCP exhibited intense pain aversion accompanied by the up-regulated BDNF expression in the rACC. Additionally, the pain aversion of BCP rats was reduced while blocking the BDNF-TrkB. Furthermore, the expression of NR2B and phosphorylated ERK (pERK)/phosphorylated CREB (pCREB) were up-regulated with the development of pain aversion, whereas the use of NR2B blocker Ro25-6981, or ERK inhibitor U0126 could reduce the pain aversion. The expression of NR2B and pERK/pCREB were up-regulated after exogenous BDNF was injected into the rACC, whereas the expression levels of NR2B and pERK/pCREB were down-regulated after blocking the BDNF-TrkB signaling. In conclusion, the BDNF-TrkB signaling in the rACC mediates the generation of aversion in rats with BCP, which requires the involvement of NR2B and the ERK-CREB signaling pathway., (Copyright © 2022. Published by Elsevier Inc.)

Objective: Cancer-induced bone pain (CIBP) is a kind of pain with complex pathophysiology. Proteinase-activated receptor 2 (PAR-2) is involved in CIBP. This study explored the effects of PAR-2 on CIBP rats., Methods: CIBP rat model was established by injecting Walker 256 rat breast cancer cells into the left tibia of female Sprague-Dawley rats and verified by tibial morphology observation, HE staining, and mechanical hyperalgesia assay. CIBP rats were injected with PAR-2 inhibitor, ERK activator, and CREB inhibitor through the spinal cord sheath on the 13th day after operation. CIBP behaviors were measured by mechanical hyperalgesia assay. On the 14th day after operation, L4-5 spinal cord tissues were obtained. PAR-2 expression, co-expression of PAR-2 and astrocyte marker GFAP, GFAP mRNA and protein levels and the ERK pathway-related protein levels were detected by Western blot, immunofluorescence double staining, RT-qPCR, and Western blot., Results: CIBP rats had obvious mechanical hyperalgesia and thermal hyperalgesia from the 7th day after modeling; mechanical hyperalgesia threshold and thermal threshold were decreased; PAR-2 was increased in spinal cord tissues and was co-expressed with GFAP. PAR-2 silencing alleviated rat CIBP by inhibiting astrocyte activation. p-ERK/t-ERK and p-CREB/t-CREB levels in CIBP spinal cord were elevated, the ERK/CREB pathway was activated, while the ERK/CREB pathway was inhibited by PAR-2 silencing. The alleviating effect of PAR-2 inhibitor on hyperalgesia behaviors in CIBP rats were weakened by ERK activator, while were partially restored by CREB inhibitor., Conclusions: PAR-2 knockdown inhibited the ERK/CREB pathway activation and astrocyte activation, thus alleviating CIBP in rats., (© 2022. The Author(s).)

Cancer-induced bone pain (CIBP) treatment remains a clinical challenge because the pathophysiological mechanisms are not fully understood. Recently, it was verified that shifting microglial polarization toward the M2 phenotype reveals a potential strategy for CIBP treatment. Naringenin, a natural flavone flavonoid, has been reported to have antioxidant, anti-inflammatory and neuroprotective properties. However, the role of naringenin on regulating microglial polarization in CIBP rats and the molecular mechanisms participating in this process have not been fully clarified. Herein, we investigated the potential effect of naringenin on M1/M2 microglial polarization and further explored the potential mechanisms of this action. Our study demonstrated that intraperitoneal administration of naringenin could upregulate the antioxidative molecule glutathione peroxidase 4 (GPx4) level in the spinal cord, as well as bone cancer-induced mechanical allodynia in rats. Moreover, naringenin treatment also suppressed microglia-mediated neuroinflammation by downregulating the phosphorylation of nuclear factor κB (NF-κB) p65 expression and promoting microglial polarization toward the M2 phenotype in CIBP rats. The promoting effects mediated by naringenin on M1/M2 microglial polarization are dependent on the serine/threonine protein kinase adenosine monophosphate-activated protein kinase (AMPK)/proliferator-activated receptor γ coactivator-1α (PGC-1α) signaling pathway. Inhibition of AMPK activation with the classical AMPK inhibitor Compound C attenuated this effect of naringenin. These results improved the understanding of the anti-inflammatory property of naringenin on microglial polarization, which might provide new alternative avenues for CIBP treatment., (Copyright © 2022 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

The tumor microenvironment is a complex milieu where neurons constitute an important non-neoplastic cell type. From "cancer neuroscience," the crosstalk between tumors and neurons favors the rapid growth of both, making the cancer-nerve interaction a reciprocally beneficial process. Thus, cancer-nerve crosstalk may provide new targets for therapeutic intervention against cancer and cancer-related symptoms. We proposed a nerve-cancer crosstalk blocking strategy for metastatic bone cancer pain treatment, achieved by Mg/Al layered-double-hydroxide nanoshells (Mg/Al-LDH) with AZ-23 loaded inside and alendronate decorated outside. The pain-causing H + is rapidly eliminated by the LDH, with neurogenesis inhibited by the antagonist AZ-23. As positive feedback, the decreased pain reverses the nerve-to-cancer Ca 2+ crosstalk-related cell cycle, dramatically inhibiting tumor growth. All experiments confirm the improved pain threshold and enhanced tumor inhibition. The study may inspire multidisciplinary researchers to focus on cancer-nerve crosstalk for treating cancer and accompanied neuropathic diseases., (© 2022 Wiley-VCH GmbH.)

Background: Noncoding microRNAs have emerged as critical players of gene expression in the nervous system, where they contribute to regulating nervous disease. As stated in previous research, the miR-155-5p upregulation happens in the spinal cord at the nociceptive state. It was unclear if miR-155-5p is linked to bone cancer pain (BCP). Herein, we aimed at investigating the miR-155-5p functional regulatory function in BCP process and delineating the underlying mechanism., Methods: The miRNA-155-5p levels and cellular distribution were determined by RNA sequencing, fluorescent in situ hybridization (FISH), and quantitative real-time PCR (qPCR). Immunoblotting, qPCR, dual-luciferase reporter gene assays, immunofluorescence, recombinant overexpression adeno-associated virus, small interfering RNA, intraspinal administration, and behavioral tests were utilized for exploring the downstream signaling pathway., Results: The miR-155-5p high expression in spinal neurons contributes to BCP maintenance. The miR-155-5p blockage via the intrathecal injection of miR-155-5p antagomir alleviated the pain behavior; in contrast, upregulating miR-155-5p by agomir induced pain hypersensitivity. The miR-155-5p bounds directly to TCF4 mRNA's 3' UTR. BCP significantly reduced protein expression of TCF4 versus the Sham group. The miR-155-5p inhibition relieved the spinal TCF4 protein's down-expression level, while miR-155-5p upregulation by miR-155-5p agomir intrathecal injection decreased TCF4 protein expression in naïve rats. Additionally, TCF4 overexpression in BCP rats could increase Kv1.1. Moreover, TCF4 knockdown inhibited Kv1.1 expression in BCP rats. Indeed, TCF4 and Kv1.1 were co-expressed in BCP spinal cord neurons., Conclusion: The study findings stated the miR-155-5p pivotal role in regulating BCP by directly targeting TCF4 in spinal neurons and suggested that miR-155-5p could be a promising target in treating BCP.